Updated stock handling to allow checking for valid allocations

oscar/apps/order/processing.py

@@ -64,6 +64,17 @@ class EventHandler(object):
         """
         self.create_payment_event(order, event_type, amount, lines, line_quantities, **kwargs)
 
+    def are_stock_allocations_available(self, lines, line_quantities):
+        """
+        Check whether stock records still have enough stock to honour the
+        requested allocations.
+        """
+        for line, qty in zip(lines, line_quantities):
+            record = line.product.stockrecord
+            if not record.is_allocation_consumption_possible(qty):
+                return False
+        return True
+
     def consume_stock_allocations(self, order, lines, line_quantities):
         """
         Consume the stock allocations for the passed lines

oscar/apps/partner/abstract_models.py

@@ -6,6 +6,7 @@ from django.utils.translation import ugettext_lazy as _
 from django.utils.importlib import import_module as django_import_module
 
 from oscar.core.loading import get_class
+from oscar.apps.partner.exceptions import InvalidStockAdjustment
 DefaultWrapper = get_class('partner.wrappers', 'DefaultWrapper')
 
 
@@ -118,6 +119,9 @@ class AbstractStockRecord(models.Model):
         self.num_allocated += quantity
         self.save()
 
+    def is_allocation_consumption_possible(self, quantity):
+        return quantity <= min(self.num_allocated, self.num_in_stock)
+
     def consume_allocation(self, quantity):
         """
         Consume a previous allocation
@@ -125,19 +129,16 @@ class AbstractStockRecord(models.Model):
         This is used when an item is shipped.  We remove the original allocation
         and adjust the number in stock accordingly
         """
-        if quantity > self.num_allocated:
-            raise ValueError('No more than %d units can be consumed' % self.num_allocated)
+        if not self.is_allocation_consumption_possible(quantity):
+            raise InvalidStockAdjustment('Invalid stock consumption request')
         self.num_allocated -= quantity
-        if quantity >= self.num_in_stock:
-            self.num_in_stock = 0
-        else:
-            self.num_in_stock -= quantity
+        self.num_in_stock -= quantity
         self.save()
 
     def cancel_allocation(self, quantity):
-        if quantity > self.num_allocated:
-            raise ValueError('No more than %d units can be cancelled' % self.num_allocated)
-        self.num_allocated -= quantity
+        # We ignore requests that request a cancellation of more than the amount already
+        # allocated.
+        self.num_allocated -= min(self.num_allocated, quantity)
         self.save()
 
     @property

oscar/apps/partner/exceptions.py

@@ -4,3 +4,7 @@ class ImportError(Exception):
 
 class CatalogueImportError(Exception):
     pass
+
+
+class InvalidStockAdjustment(Exception):
+    pass

oscar/apps/partner/tests/models.py

@@ -52,6 +52,12 @@ class StockRecordTests(TestCase):
         self.assertEqual(1, self.stockrecord.num_allocated)
         self.assertEqual(10, self.stockrecord.num_in_stock)
 
+    def test_cancelling_allocation_ignores_too_big_allocations(self):
+        self.stockrecord.allocate(5)
+        self.stockrecord.cancel_allocation(6)
+        self.assertEqual(0, self.stockrecord.num_allocated)
+        self.assertEqual(10, self.stockrecord.num_in_stock)
+
 
 class DefaultWrapperTests(TestCase):